Double Mash BIAB

So I have 5 batches of BIAB all grain under my belt, but I want to brew something BIG. So I decided to try a double mash. Basically mash half of the grain, drain the bag, and then repeat with the other half of the grain in another bag.

I have
18lb 2-row
2lb - 40L
1lb - Carapils

Im doing this tomorrow. Will reply with results. Any thoughts? Have you heard of anyone doing this?

Looking forward to reading about your results. Will you measure gravity after both mashes? I am curious if the second mash will differ in efficiency. I have read here about other brewers trying the same technique but I've not seen results reported before.

What are you going to do with the first five gallons of wort while you mash the second half?

Sounds interesting to say the least!

ChadRabbit said:

What are you going to do with the first five gallons of wort while you mash the second half?

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My understanding of this technique is that he's not going to do anything with the wort. It will stay in the kettle. Basically he is going to mash once with water, then mash again using the wort from the first mash instead of water.

yep I am going to mash in the same water. anything else would defeat the purpose.

Pardon my ignorance, but why not just do the 21 lbs in one bag? What is the limiting factor?

Yeah, I would like to know how this works out for you as welll! I can't do more than about 12 lbs. of grain with my current setup.

Due to kettle size?

I've done this for an English Barleywine.

I did a write-up on my blog here so there is a lot more detail/pics there.

To sum it up:
24 lbs Marris Otter
.5 lbs Simpson's Medium Crystal
.5 lbs Simpson's Extra Dark Crystal

Divided evenly and mashed at 148 for 75 minutes for each mash.

Mash 1 gravity 1.038
Mash 2 gravity 1.078

This was before I had my mill and I was averaging about 65-70% efficiency with LHBS crush.

OG 1.102

The reason to split is to improve efficiency. Sure you could mash it all in one bag with the right size kettle, but the more grain you use the lower your efficiency (especially true with BIAB in my experience). What's another 60-75 minutes for a 2nd mash when you're brewing a big beer?

mtnagel said:

Due to kettle size?

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There is a limit on how much grain those bags can hold, especially when you consider that they need to be lifted out of mash water with the soaked grains. At a certain weight, you risk having the bag rip open. I try to keep my BIAB grain quantities to around 11-12lbs. I'm planning on doing a double mash this Friday for a high gravity Old Ale. My plan is to do two completely separate mashes, transferring the first to a bucket and doing the second one from scratch, then combining the wort and proceeding as normal.

brewing a batch of berliner weisse now soon to be followed by my double mash. its gonna be an imperial ipa if you didn't get that from the grain bill. im gonna use mix of challenger chinook and Zeus hops. haven't decided on the exact schedule yet.